This is an answer given by the Shaykh to the issue of requesting the supplication of those who have passed away and entered the barzakh. The Shaykh was asked (during his explanation of Aqidah al-Tahaawiyyah), in the print version 2/1029 (Dar al-Mawaddah, Egypt):

Yes, it is major shirk because the Prophet (sallallaahu alayhi wasallam) is not to be called upon after his death. Requesting supplication from the dead and requesting (their) supplication (for them to) request rescue and sending of rain, meaning, that he supplicates to Allaah that He grants relief or he supplicates to Allaah to forgive (the person making the request), that he supplicates to Allaah to give (to that person) and what is like this, all of it is enters into the word "du'a" (supplication) and Allaah, the Mighty and Majestic said, "And the mosques are for Allaah, so do not invoke anyone alongside Allaah" (72:18).

And the one who says that this form, which is to request the supplication (of the deceased) is excluded from that (type of) request through which shirk is actually shirk, then he has demolished the entire foundation of Tawheed in this particular topic.

For all types of request (talab), requesting supplication, meaning requesting supplication from the dead or requesting aid and what is like that, all of it is included within the same subject area, which is (making) request (talab), and requesting is supplicating (du'a), so it is included within His, the Most High's saying, "And whoever invokes besides Allah, any other ilah (god) of whom he has no proof then his reckoning is only with his Lord. Surely, the disbelievers will not be successful." (23:117) and it is also included within His saying, "And the mosques are for Allaah, so do not invoke anyone alongside Allaah" (72:18) and into His saying "And those, whom you invoke or call upon instead of Him, own not even the thin membrane over the dateŭstone" (35:13) and other similar verses.

Hence, making this distinction clashes with the evidence and whoever understood from some of the speech of our Scholars (this) separation or that this requesting of supplication from the dead is a bid'ah (innovation), this does not mean it is not (at the same time) shirk, rather it is an innovated (form) of shirk, with the meaning that the people of Jaahiliyyah did not used to perform this (particular type of shirk). They used to seek nearness to (their deities) so they in turn would supplicate for them. However, that the dead are requested to supplicate, this is a bid'ah, it was not present originally, neither with the people of Jaahiliyyah and nor with the Muslims, then it occurred, and so it is an innovation no doubt (from this angle), however it is an innovation of shirk and kufr. And this is the (very) meaning of shafaa'ah (intercession), what is the meaning of intercession, that (intercession) which if a person seeks from other than Allaah he becomes a mushrik? intercession (means) to request supplication, requesting supplication from the dead, this is (the meaning) of intercession.